Plants with imidazolinone-resistant ALS

Abstract

Acetolactate synthase (ALS), a key enzyme in the biosynthesis of valine, leucine and isoleucine in plants is inhibited by herbicides comprising imidazolinones. The present invention relates to Arabidopsis thaliana genes encoding a mutant acetolactate synthase (ALS) enzyme that is specifically resistant to imidazolinone herbicides. Exemplary of these genes are DNA sequences which encode an amino acid substitution at position 122 or an amino acid substitution at position 205 of the wild-type ALS enzyme in Arabidopsis thaliana , ecotype Columbia or an amino acid substitution at position 205 of the wild-type ALS enzyme in Arabidopsis thaliana , ecotype Landsberg erecta. The mutant ALS genes can be used to transform plants to herbicide resistance; in this regard, the invention also provides host cells and vectors containing the gene, which cells and vectors are useful in the transformation process. The mutant ALS genes is commercially useful, when used to impart imidazolinone resistance to a crop plant; thereby permitting the utilization of the imidazolinone or analogous herbicide as a single application at a concentration which ensures the complete or substantially complete killing of weeds, while leaving the transgenic crop plant essentially undamaged.

What we claim is:  
     
         1 . A nucleic acid molecule encoding functional ALS which has (a) an alanine-to-threonine substitution at amino acid sequence position 122, or (b) an alanine-to-valine substitution at amino acid sequence position 205, relative to the amino acid sequence alignment of FIGS. 1 and 2.  
     
     
         2 . A transformation vector comprising the nucleic acid molecule of  claim 1 .  
     
     
         3 . A host cell comprising the nucleic acid molecule of  claim 1 .  
     
     
         4 . A host cell of  claim 3  which is a plant cell or a bacterial cell.  
     
     
         5 . A host cell of  claim 4  which is an imidazolinone-resistant plant selected from the group consisting of  Arabidopsis thaliana , maize, soybean, wheat, cotton, canola, rice and sunflower.  
     
     
         6 . A host cell of  claim 4  which is recombinant.  
     
     
         7 . A transformed plant exhibiting imidazolinone resistance having a nucleic acid molecule which comprises: (a) an exogenous promoter region which functions in a plant cell to cause the production of a mRNA molecule; (b) a structural nucleic acid molecule encoding functional ALS comprising an amino acid sequence of SEQ ID NO: 3 or SEQ ID NO: 4 or SEQ ID NO: 26 or a homolog thereof having an alanine-to-threonine substitution at position 122 or an alanine-to-valine substitution at position 205, and (c) a 3′ non-translated sequence that functions in the plant cell to cause termination of transcription and addition of polyadenylated ribonucleotides to a 3′ end of the mRNA molecule.  
     
     
         8 . The transformed plant according to  claim 7 , wherein said plant is selected from the group of rice, cotton, wheat, canola, maize, soybean and  Arabidopsis thaliana.    
     
     
         9 . The transformed plant of  claim 8  wherein the structural nucleic acid molecule has a nucleic acid sequence of SEQ ID NO: 1 or SEQ ID NO:2 or SEQ ID NO: 25 or homologs thereof which encode an ALS with an alanine-to-threonine substitution at position 122 or an alanine-to-valine substitution at position 205.  
     
     
         10 . A method of conferring imidazolinone-specific resistance to a plant cell which comprises providing the plant cell with the nucleic acid sequence of  claim 1 .  
     
     
         11 . A nucleic acid construct comprising the sequence of  claim 1  linked to a gene encoding an agronomically useful trait.  
     
     
         12 . A method of conferring imidazolinone resistance to a plant comprising providing said plant with a nucleic acid molecule of  claim 1 .  
     
     
         13 . A method for determining the imidazolinone tolerance of a plant comprising detecting the presence of a nucleic acid molecule of  claim 1 .  
     
     
         14 . A method for introgressing an agronomically useful trait into a plant comprising: (a) constructing a vector comprising SEQ ID NO: 1 or SEQ ID NO: 2 or SEQ ID NO: 25 or homologs thereof which encode an alanine-to-threonine substitution at position 122 or an alanine-to-valine substitution at position 205, operably linked to a gene for said agronomically useful trait; (b) transforming said vector into plant cells; (c) growing plant; and (d) testing plant for introgression of said trait by selecting plants with imidazolinone resistance.  
     
     
         15 . A method using imidazolinone resistance as a selectable marker in a cell or organism wherein said resistance is provided by nucleic acid molecule of  claim 1 .  
     
     
         16 . A set of primer pairs for amplifying an ALS gene or fragment thereof comprising at least two oligonucleotides selected from the group consisting of SEQ ID NO: 5 through SEQ ID NO: 24.